The present invention relates to apparatus for accumulating stacks of paper sheets or the like. More particularly, the invention relates to improvements in apparatus of the type having (a) a cross cutter which repeatedly severs several superimposed running webs of paper or a like flexible material so as to form a series of groups of overlapping sheets wherein the number of sheets equals the number of overlapping webs, (b) means for gathering several groups into layers of superimposed sheets, and (c) means for accumulating several layers into discrete stacks.
Commonly owned German Offenlegungsschrift No. 31 27 569 and commonly owned copending U.S. Pat. No. 4,474,093 of Neubuser et al. discloses an apparatus wherein the layers which consist of several groups of superimposed sheets are removed from the gathering station by a transfer device having a tongs with jaws arranged to engage the topmost and lowermost sheets of a layer and a camshaft carrying several rotary cams which initiate and control the movements of the transfer device between the gathering station and a removing conveyor which delivers layers of the stacking station. The arrangement is such that the transfer of a layer takes place subsequent to the gathering of several groups of sheets into such layer, i.e., the number of machine cycles (each machine cycle involves the making of a group of r sheets) is several times the number of working cycles (each working cycle involves the transfer of a layer from the gathering station into the range of the aforementioned removing conveyor). The apparatus of Neubuser et al. further comprises means for varying the number of machine cycles per working cycle in order to enhance the versatility of the apparatus by rendering it possible to accumulate stacks having widely different numbers of sheets.
Apparatus of the type disclosed by Neubuser et al. are used in modern production lines wherein stacks of overlapping paper sheets of the like must be accumulated at a high frequency, for example, to be introduced into discrete cardboard boxes or to be converted into calendars, exercise books, steno pads and/or other stationery products. A first step in speeding up the formation of successive stacks is the provision of a cross cutter which forms groups of overlapping sheets wherein the number r of sheets equals the number of overlapping running webs which are severed during each machine cycle. A group constitutes the smallest unit for the assembly of a stack, i.e., the number of sheets in a stack is necessarily a whole multiple of the number of sheets in a single group. As mentioned above, the groups are accumulated into layers each of which contains several groups, and such layers are thereupon transferred to the stacking station where a certain number of layers is accumulated into a complete stack. The removal of finished stacks from the stacking station and the preparation of the stacking station for accumulation of the next stack takes up a certain interval of time which cannot be shortened at will and which imposes limits upon the number of stacks that can be accumulated per unit of time. Thus, the frequency of the aforediscussed working cycles cannot be increased beyond that which is permissible in view of the minimum duration of an interval of removal of a finished stack from and of preparation of the stacking station for reception of the first layer of the next-following stack.
The accumulation of groups of sheets into layers is intended to provide longer intervals of time for removal of a stack from the stacking station. This will be readily appreciated by bearing in mind that the interval for removal of a freshly formed stack is much shorter if such stack is formed of a large number of discrete groups (of e.g., six sheets each) than if the stack is formed or a smaller number of successive layers each of which contains several groups of sheets (e.g., a total of thirty sheets).
The reasons for varying the number of machine cycles per working cycle during the formation of a stack are as follows: If the stack is accumulated from a succession of layers rather than from a succession of groups, and the number of groups per layer is always the same, the number of sheets in each of the stacks is necessarily a whole multiple of the number of sheets per layer. For example, if a layer invariably contains thirty sheets, the number of sheets in a layer can be a whole multiple of thirty which greatly limits the versatility of the stack forming apparatus. However, if a stack is assembled of several sets of layers each of which contains a different number of sheets, the number of sheets per stack can be varied within a much wider range, i.e., the total number of sheets per stack is then a multiple of the number r of sheets in a group.
In the apparatus of Neubuser et al., a first prime mover is utilized to drive the cross cutter and a discrete second prime mover is provided to drive the camshaft for the transfer device which delivers successive layers from the gathering station into the range of the aforementioned removing conveyor. A computer is provided to synchronize the operation of the cross cutter with that of the transfer device.